1. Field of the Invention
This invention relates generally to a method for cutting an aperture in a device, and more particularly to a method for cutting an aperture in a device comprising a wall having first and second opposing surfaces, and a third surface separated from said wall. The method is suitable for cutting apertures in a wall of narrow pieces of tubing, and it will be convenient to hereinafter disclose the invention in relation to that exemplary application. It is to be appreciated, however, that the invention is not limited to that application.
2Description of the Prior Art
Many devices manufactured today require the cutting of an aperture in a wall thereof. Devices such as injector nozzles, syringe needles, medical stents, fluid/air control valves and small collets all have bores or openings running therethrough which define at least one wall surrounding the bore or opening. In each of these devices, at least one aperture is required to be cut through the wall, so as to thereby enable, for example, the communication of a fluid with the bore in the device, or so as to alter the flexibility or other mechanical properties of the device. Moreover, many of these devices are small and require the aperture to be cut with a high degree of precision.
One existing method of accurately cutting such an aperture uses a process called Electrical Discharge Machining (EDM). The EDM process uses spark erosion to cut the aperture in the device, which, using this process, must be metallic. The device acts as a cathode, whilst the anode is provided by an electrode maintained very close to the surface of the device. Both the anode and the cathode are submerged in a dielectric liquid. High local temperatures are produced by passing a current through the gap between the device and the electrode, thus detaching and repelling particles from the device.
The EDM process can be classified according to two related techniques: a wire cutting technique and a sinker technique. In the wire cutting technique, a starting hole has to be firstly drilled in the wall of the device at the location where the cutting of the aperture is to commence. A wire, typically between 0.1-0.2 mm in diameter, is used as the anode and must be passed through the drilled hole. Current is then passed between the wire and the device so that particles from the device are detached. The wire is moved through the thickness of the wall, at a speed limited by the rate of particle detachment, so as to define the form of the aperture.
In the sinker technique, a copper or graphite electrode is placed close to the exterior surface of the wall through which the aperture is to be cut. Current is passed between the device and the electrode so that particles from the wall of the device are detached, the resulting aperture having the same form as that of the electrode. While this technique does not require the preliminary drilling of a hole, the electrode must however be precisely shaped to that of the desired aperture.
It can thus be understood that both EDM techniques are time and labour intensive in their preparation and in addition are limited in their cutting speed.
It is also known to cut apertures through the walls in such devices by the process of chemical etching. According to this process, a mask is placed on the exterior surface of the device, which mask has an opening defining the form of the aperture to be cut. When placed in a chemical bath, the aperture is etched though the device in the region of the opening of the mask. A separate mask must be produced for each device to be treated. Additionally, while chemical etching is often used in the treatment of flat, thin surfaces, the difficulty in the production and location of appropriate masks means that this process is not well suited to the cutting of apertures in walled-devices.
Milling is another process which is sometimes used to cut apertures in the walls of such devices. However the use of this process requires the removal of material by force from the wall of a device. Such force can cause the deformation of the device, particular in small, delicate devices such as syringe needles and injection nozzles.